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LIDAR detector maps out planets

Scientists in the US are developing silicon detectors that can =
distinguish=20
objects on a planet's surfaces that are centimetres apart =E2=80=94 even =
when the planet=20
is hundreds of miles away. The group from the Rochester Institute of =
Technology=20
hope that their device, which uses light detection and ranging (LIDAR), =
will=20
help NASA spacecraft to land safely.

"Our motivation is to develop imaging detector technology capable of=20
obtaining three dimensional maps of surfaces and atmospheric =
properties," Don=20
Figer, a researcher from the Rochester Imaging Detector Laboratory, told =
optics.org. "The super-rich maps will be important for =
determining where=20
to land on planets and moons. They will also provide a very detailed =
historical=20
record of surface modification on these bodies."

Existing LIDAR detectors generally have a single pixel that has to be =
moved=20
across a scene in order to build up an image. Now, however, the US team =
hopes=20
that using two-dimensional arrays of LIDAR pixels will allow faster =
mapping and=20
better resolution.

"We aim to develop 2D arrays of pixels up to the megapixel scale, =
which will=20
provide images at higher spatial resolutions," commented Figer. "In =
addition,=20
the device is very fast =E2=80=94 responding in hundreds of picoseconds, =
which allows=20
ranging resolutions in the order of centimetres."

The device will consist of a 2D continuous array of light-sensing =
elements=20
connected to high-speed circuits. The new detector can be used to =
measure=20
distance, speed and planetary rotation as well as atmospheric properties =
such as=20
pressure, temperature, chemical composition and ground-layer properties. =

"The detector works by using techniques such as differential =
absorption=20
LIDAR," explained Figer. "These methods rely on the ability to measure =
frequency=20
shifts, differential widths and depths of absorption features such as =
those=20
observed in moving collections of water vapour or ozone."

The team will initially develop devices that can detect a broad range =
of UV=20
up to 1 =C2=B5m before extending the technology to cover other =
wavelengths. "A=20
key problem to overcome is to implement a design that allows various =
types of=20
semiconductors to be used in the light-sensitive portion of the =
detector," he=20
said.